1. Field of the Invention
The present invention generally relates to automotive safety restraint systems for motor vehicles. More specifically, the invention relates to an active three-point seat belt system having a retractor incorporating a pretensioning function for two belt sections terminating at the retractor frame.
2. Description of Related Art
Motor vehicle seat belt restraint systems are available in a number of configurations. The most common in modern automobiles is the so-called three point type having a single shoulder belt and a lap belt. This configuration uses either a single continuous length of belt webbing, provided with a single retractor, or separate lap and shoulder belt sections each having their own retractor integrated together or separate.
In the single retractor arrangement, a latch plate slides along the belt. One end of the belt is attached to a first anchor point secured to the vehicle on one side of the seat. The other end is attached to a rotatable spool retractor secured to the vehicle at a second anchor point which, for example, can be on the floor pan, side pillar, or seat structure. To secure an occupant, the belt latch plate is inserted and fastened into a buckle, also fixed to an anchor, and the belt slides through the latch plate as the occupant fastens and unfastens the seat belt.
The dual retractor belt arrangement has two belts each individually attached to the latch plate at one end and secured to a separate retractor spool at the other. In some vehicles with dual retractors, each retractor is remotely mounted, independent of the other. Each retractor spool separately pays out or draws in the lap and shoulder belt webbing as necessary. This configuration is more costly due to the provision of an additional retractor. In addition, assembly and mounting within the vehicle is more complex because each retractor may be independently mounted to the vehicle. However, dual retractors are desirable in some applications to meet performance requirements, and for application in premium vehicles due to the additional comfort and convenience features such systems can provide for the occupants. Some dual retractor systems have two spools carried in a single frame.
A further feature of modern belt restraint systems is the inclusion of a pretensioning system. Pretensioning systems may be activated by a control system that, for example, senses emergency braking or, similar to an airbag deployment system, detects an actual or impending vehicle collision. If the system detects an appropriate event, the pretensioning system causes the retractor spool or spools to quickly draw-in slack from the belts, thereby enabling the restraint system to engage the occupant early in the collision sequence.
In a single belt system, the pretensioning device may be coupled to a single retractor spool. Performance can be enhanced for such systems if a so-called lap pretensioner attached to the lap belt anchorage point linearly retracts webbing from the lap belt while the single retractor also acts on the belt. For dual spool retractor systems, if pretensioning is desired on both spools, the system must have devices coupled to both spools. This is a more complex and costly configuration since the control system must be configured to actuate both devices. One such approach is to use two separate pretensioning systems, each dedicated to act on one of the two retractor spools.
Various designs of belt pretensioners are known. One type, known as a roto-pretensioner, incorporates a series of balls in a gas duct which are driven by the activation of a micro-gas generator to engage with a sprocket to wind the retractor spool to retract the belt. In a dual retractor system, two such roto-pretensioners may be required.
Another type of pretentioner uses an electric motor to drive one or more spools. These pretensioners have added flexibility since the control system may be configured to retract slack or otherwise control the spools in non-emergency situations. For example, the system may be configured to retract the slack in the belts when an occupant exits the vehicle. However, existing electric motor driven retractors require an independent electrical motor for each retractor spool. This results in additional cost and complexity. Due to the rapid response requirements of pretensioning, electric motor driven retractors may also have pryrotechnic pretensioner mechanisms.
Mentioned previously are linear retractors which are pyrotechnically actuated and are usually mounted to a vehicle anchorage point to retract a buckle or guide loop of a belt system. Such systems may act in conjunction with or instead of retractor based pretensioning systems. In an effort to provide greater total pretensioning effects, two (or more) pretensioning systems can be provided to act on a belt system for restraining an occupant.
In addition to the considerations previously mentioned, new US NCAP criteria place increasingly stringent requirements on the performance of belt and passive occupant restraint systems. Including in such requirements are those related to chest deflection and femur loads measured on standardized crash test dummies during crash test studies. Dual spool retractors having pretensioning systems for both spools have been shown to enhance ability to meet these increasingly stringent requirements. When providing such systems, it is desirable to reduce the number of components and the complexity of such systems
In view of the above, there exists a need for a seat belt retractor device providing pretensioning functions for two spools or otherwise for two belt sections terminating at the retractor, and provided in a manner which is cost-effective and capable of meeting performance requirements.